First metatarsophalangeal joint synovial hypertrophy associated with vitamin D status in type 2 diabetes mellitus: An ultrasound-graded study.

Background: The existing semi-quantitative ultrasound grading system inadequately evaluates synovial hypertrophy at the dorsal recess of the first metatarsophalangeal joint (MTPJ). Vitamin D deficiency is prevalent in type 2 diabetes mellitus (T2DM) and may influence joint inflammation. This study hypothesizes that serum 25-hydroxyvitamin D [25(OH)D] levels are inversely associated with synovial hypertrophy severity of the first MTPJ in patients with T2DM.

Aim: To refine ultrasound grading for the first MTPJ synovial hypertrophy and investigate its association with vitamin D in T2DM.

Methods: This cross-sectional study included 56 patients (112 MTPJs) with T2DM from Shenzhen Traditional Chinese Medicine Hospital. Synovial hypertrophy was evaluated using a refined semi-quantitative ultrasound grading system focusing on the dorsal recess overlying the metatarsal bone. Serum 25(OH)D levels were measured. Logistic regression and threshold analyses assessed associations between vitamin D status and hypertrophy severity.

Results: Of 112 joints assessed, 98 exhibited synovial hypertrophy (grade 1: 40; grade 2: 50; grade 3: 8). The refined grading system demonstrated strong intra- and inter-observer reliability (intraclass correlation coefficients = 0.79 and 0.73, respectively). Lower serum 25(OH)D (< 24.3 ng/mL) was independently associated with moderate-to-severe hypertrophy [odds ratio (OR) = 0.83; P = 0.0163]. Vitamin D deficiency significantly increased the likelihood of moderate-to-severe hypertrophy compared with non-deficiency (OR = 3.86; P = 0.0422). Threshold analysis identified 23.8 ng/mL as a critical serum 25(OH)D level, below which each increment reduced moderate-to-severe hypertrophy risk by 21% (OR = 0.79; P = 0.0078).

Conclusion: The refined ultrasound grading system demonstrated strong reliability. Serum 25(OH)D may serve as a protective factor against the severity of synovial hypertrophy in T2DM patients with lower 25(OH)D levels.